Adenovirus Serotypes 8, 19, & 37
Adenovirus (Ad) serotypes 8, 19, and 37 are the most common causes of epidemic keratoconjunctivitis (EKC). There is a specific amino acid sequence/conformation that allows the tropogens of these Ad serotypes to preferentially bind and to infect human conjunctival cells of the eye.
Once these Ad serotypes have successfully infected conjunctival cells, symptoms appear somewhere between 5 and 12 days. The onset of EKC is acute and within the first 2 days, the conjuctiva becomes infiltrated, chemotic, and hyperemic, with the possibility of hemorrhage. On the 3rd day, follicles form on the fornix and the tarsal conjunctiva, and they may remain there for several weeks. At this time, the patient also has red eye, ocular irritation, foreign body sensation, and watery discharge. Accompanying symptoms can vary depending on the age of the individual infected; systemic symptoms such as fever, sore throat, and gastrointestinal disturbances are more commonly seen in infected children than adults. Although the viral infection begins unilaterally, both eyes of the individual usually become involved because the highly infectious nature of the virus facilitates viral transmission to the other, healthy eye.
Frequently, the cornea is also infected (keratitis), in addition to the infection of the conjunctiva. This happens about 7 to 10 days after the onset of conjunctivitis. Keratitis is marked by the presence of epithelial erosions on the corneal surface. The keratitis can last days to weeks, or it can persist even longer, leading to epithelial infiltrates. The subepithelial infiltrates are believed to be immunogenic, (consisting of macrophages, lymphocytes, plasma cells) and they usually disappear 2 weeks after the initial onset of the keratitis. However, these infiltrates have the potential to become chronic if they persist for a prolonged period of time (up to a year or longer, and could even be longer than 10 years). Chronic infiltration and edema of the subepithelium due to the inflammatory response can damage the superficial stroma of the eye as well as Bowman's layer. Subepithelial lesions formed may lead to corneal scarring, causing vision loss and photophobia.
Adenovirus serotypes 8, 19, and 37 are highly infectious and transmissible because the nature of the virus allows it to survive in many environments. For instance, standard disinfectants like ammonia does inactivate the virus, and viruses left on many surfaces can remain infectious for up to 35 days. There is also a very long period of sheddingæ 3 days prior to the onset of symptoms and 14 days after symptoms manifestæ that gives the virus time to spread from one individual to another. These characteristics allow these adenoviral serotypes to be transmitted in a number of ways, with speed and efficiency. This virus is most commonly transmitted by fomites, such as instruments like tonometers used in eye clinics and hospitals. It can also be spread by direct contact between people in close proximity to one another (such as in hospitals, schools, prisons), hand-to-eye transmission, waterborne transmission (such as in public pools), and in some cases serotype 19 may even be sexually transmitted. For these reasons, adenovirus serotypes 8, 19, and 37 quickly and easily infect many people at a time, resulting in epidemic keratoconjunctivitis.
Epidemic keratoconjunctivitis is usually a self-limited disease, and treatment is mostly symptomatic. There are no antiviral therapies that have proven to be effective in the clinical treatment of this disease, though adenoviruses have shown some sensitivity to idoxuridine, cidofovir, and trifluorothymidine in vitro. Supportive therapy, such as cold compresses, artificial tears, topical vasoconstrictors, and systemic analgesics, can be used to relieve symptoms. In the case of chronic infiltration of the epithelium, corticosteroids have been shown to be effective in suppressing conjunctival inflammatory signs, relieving symptoms, and causing the corneal infiltrates to disappear. Corticosteroids (like prednisolone acetate) might be used as a means to limit the amount of destruction to the cornea by inhibiting epithelial infiltration, but they should only be used sparingly because they may interfere with viral clearance.
Since there are no effective treatments for keratoconjunctivitis and since a vaccine for these adenovirus serotypes does not exist, prevention is critical. The first precautionary measures should be taken to prevent nosocomial transmission. Healthcare workers in ophthalmologist offices should take care to thoroughly wash their hands to avoid hand-to-eye transmission, potential fomites such as tonometers should be thoroughly disinfected with sodium hypochlorite, and infected patients should be identified and isolated. In addition, swimming pools should be properly chlorinated to avoid waterborne transmission, and people should take proper sexual precautions to avoid transmission of the virus from the genital tract to the eyes.
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Ostler BH, Bierly JR. The Cornea. Butterworth-Heinemann. 1998. pg. 303-6.